The primary goal of our studies is to identify individuals with the highest risk of lung cancer among current, ex-, and passive-smokers. Tobacco smoking continues to be a major public health problem, not only in the U.S., but also worldwide. The two major facets of the molecular epidemiology of lung cancer risk are first, the assessment of carcinogen exposure including biomarkers of effect, and second, the inherited or acquired host cancer susceptibility factors. We utilize both case-control and case-series strategies to investigate hypotheses of gene-environment interactions in lung cancer risk. We have a multi-tiered strategy for conducting our hypotheses-driven studies. Recent molecular epidemiological studies have identified polymorphisms in the XPD gene that are associated with increased risk of brain gliomas and head, neck, lung, and skin cancers. However, the functional significance of these polymorphic variants in altering cell processes such as cell cycle checkpoints, DNA repair, and apoptosis, is uncertain. We then genotyped 34 different lymphoblastoid cell lines from six CEPH/Utah pedigree families and a CEPH/French pedigree family for polymorphisms at codons 751 and 312, as assessed their apoptotic response after either UV or IR exposure. The apoptotic rates, whereas cell lines with homozygous or heterozygous Asp at codon 312 have similar apoptotic rates, cell lines with homozygous Asn at codon 312 showed a 2.5-fold increased response to UV (p=0.005; Student's t-test). This is the first report known to us of a functional polymorphism in a gene involved in DNA damage-induced apoptosis. The presence of Lys or Gln at codon 751, however, did not influence the apoptotic response to UV. The diminished apoptotic response of cells containing the 312 Asp allele could both allow the survival and selective clonal expansion of carcinogen-damaged cells, and be a mechanistic explanation for the increased risk of cancer at diverse tissue sites. Somatic p53 mutations are common in lung cancer. Active cigarette smoking is positively correlated with the total frequency of p53 mutations and G:C to T:A transversions on the nontranscribed (DNA coding) strand. Mutational hotspots within the p53 gene, e.g., codon 157, have been identified for tobacco-related lung cancer, whereas these same mutations are found rarely in other cancers. Such data implicate specific p53 mutations as molecular markers of smoking. Because limited data exist concerning the p53 mutation frequency and spectra in ex-smokers and nonsmokers, we have analyzed p53 and K-ras mutations in 126 lung cancers from a population-based case-control study of nonsmoking (n-117) or ex-smoking (n=9) women from Missouri with quantitative assessments of exposure to environmental tobacco smoke. Mutations in the p53 gene were found in lung cancers from lifetime nonsmokers (19%) and ex-smokers (67%; odds ratio, 9.08; 95% confidence interval, 2.06-39.98). All deletions were found in tumors from patients who were either ex-smokers or nonsmokers exposed to passive smoking. The G:C to A:T transitions (11 of 28; 39%) were the most frequent p53 mutations found and clustered in tumors from lifetime nonsmokers without passive smoke exposure. The incidence of K-ras codon 12 or 13 mutations was 11% (14 of 115 analyzed) with no difference between long-term ex-smokers and nonsmokers. These and other results indicate that p53 mutations occur more commonly in smokers and ex-smokers than in never-smokers. Such comparisons provide additional evidence of genetic damage caused by tobacco smoke during lung carcinogenesis. p53 mutations are common in lung cancer. In smoking-associated lung cancer, the occurrence of G:C to T:A transversions at hotspot codons, e.g., 157, 248, 249, and 273, has been linked to the presence of carcinogenic chemicals in tobacco smoke including polycyclic aromatic hydrocarbons such as benzo(a)pyrene (BP). In the present study, we have used a highly sensitive mutation assay to determine the p53 mutation load in nontumorous human lung and to study the mutability of p53 codons 157, 248, 249, and 250 to benzo(a)pyrene-diol-epoxide (BPDE), an active metabolite of BP in human bronchial BEAS-2B cells. We determined the p53 mutational load at codons 157, 248, 249, and 250 in nontumorous peripheral lung tissue either from lung cancer cases among smokers or noncancer controls among smokers and nonsmokers. A 5-15-fold higher frequency of GTCval to TTCphe transversions at codon 157 was found in nontumorous samples (57%) from cancer cases (n=14) when compared with noncancer controls (n=8; p<0.01). Tumor tissue from these lung cancer cases (38%) contained p53 mutations but were different from the above mutations found in the nontumorous pair. BEAS-2B bronchial epithelial cells exposed to doses of 0.125, 0.5, and 1.0 um BPDE, showed G:C to T:A transversions at codon 157 at a frequency of 3.5 x 10-7, 4.4 x 10-7, and 8.9 x 10-7, respectively. No mutations at codon 157 were found in the DMSO-treated controls. These data are consistent with the hypothesis that chemical carcinogens such as BP in cigarette smoke causes G:C to T:A transversions at p53 codons 157, 248, and 249, and that nontumorous lung tissues from smokers with lung cancer carry a high p53 mutational load at these codons.